1. Field of the Invention
The invention is directed to a grease loaded dampener for a grapple skidder having a pressure relief valve to prevent over compressing the friction plates.
2. Description of the Prior Art
Grapple skidders are forestry work vehicles used to haul logs in rugged terrain. The skidder is typically provided with a boom that can be manipulated into a variety of positions. A grapple is mounted to the end of the boom by a swivel link. The swivel link is pivotally coupled to the boom by a first pivot connection and pivot pin, and to the grapple by a second pivot connection and pivot pin.
Each pivot connection of the swivel link is typically provided with at least one dampener for dampening any excessive oscillations occurring in the swivel link by the swinging movement of the unloaded grapple. Typically the first pivot connection is provided with a first dampener that comprises a first set of friction plates located on a first pivot pin. The first set of friction plates are operatively coupled to the swivel link and the boom. Similarly, the second pivot connection is provided with a second dampener that comprises a second set of friction plates located on a second pivot pin. The second set of friction plates are operatively coupled to the swivel link and the grapple.
The pivot pins may be stepped pins having an enlarged portion adjacent to the pivot connection and a smaller portion on which are mounted the friction plates. The smaller portion is also provided with a threaded surface for receiving a jam nut and a retaining washer for compressing the friction plates. The operator at selected intervals tightens the jam nut with a torque wrench compressing the friction plates to ensure proper braking force. Such dampeners are disclosed in U.S. Pat. No. 4,417,759, assigned to the assignee of the present application.
Instead of a jam nut and a retaining washer to supply a compressing force on the friction plates, hydraulic and grease loaded dampeners have also been proposed. See U.S. Pat. Nos. 3,301,587 and 4,572,567. Grease loaded dampeners use pressurized grease to drive a piston against the friction plates to increase the braking force. Such a dampener is disclosed in U.S. Pat. No. 4,679,839. The operator when greasing the machine injects grease through a grease zerk into the dampener. This drives the piston towards the friction plates increasing the braking force.
Operators must periodically adjust the compression force of the jam nut on the mechanical dampener, or apply grease to the grease dampener. Many times operators over-tighten the jam nut and over-pressurize the grease dampener. This excessive compression force on the friction plates leads to accelerated wear on the friction plates and their early replacement.